This invention relates to disposable diapers having normally tacky and pressure-sensitive adhesive tape closures and is particularly concerned with composite closures (i.e., closures made with more than one tape) that can be opened and refastened without destroying either the diaper or the tape.
The invention especially relates to a thermoplastic monolayer film suitable for use as a refastenable diaper backsheet comprising a blend of polyolefins particularly polypropylene and polyethylene.
At least as early as 1955 it had been suggested to use strips of normally tacky and pressure-sensitive adhesive tape to hold conventional cloth diapers on an infant; see, e.g., Chambers U.S. Pat. No. 2,714,889 and Ekberg U.S. Pat. No. 3,221,738. A few years later, when disposable diapers became extremely popular, strips of pressure-sensitive adhesive tape were again employed as closures; see, e.g., Gellert U.S. Pat. No. 3,620,217.
A disposable diaper typically has a thin, flexible, stretchy low density polyethylene film cover, an absorbent filler on the inside of the cover, and a porous inner liner overlying the filler. Such a diaper is positioned at the crotch of an infant, the two ends of the diaper extending, respectively, toward the front and back. Adjacent edges of the diaper at each side are then either positioned next to each other or overlapped, a strip of pressure-sensitive adhesive tape being adhered to the cover at the border adjacent each of the two edges and holding the diaper closed. Because most pressure-sensitive adhesives bond firmly to the thin polyethylene diaper cover, it is almost impossible to open the tape closure without destroying the tape and/or the diaper cover in the process.
After a tape closure has been opened, it is frequently discovered that the diaper has not been soiled and hence that there is no need to replace it. If the cover has not been torn, a second strip of tape can sometimes be applied as a replacement closure, but this is often inconvenient. As a result, considerable work has been undertaken to develop a tape diaper closure that is not only capable of bonding firmly to the diaper cover, but is also capable of non-destructive removal and replacement. Closures of this type have generally involved a combination of two or more tapes, one of which remains permanently adhered to one edge of the diaper and is removably adhered to a so-called "target tape" mounted on the other edge of the diaper. Examples of such products are shown in Ness et al, U.S. Pat. No. 3,951,149, Milnamow U.S. Pat. No. 3,987,793, Feldman et al U.S. Pat. No. 3,999,546, and Richman et al U.S. Pat. No. 4,020,842.
The patents referred to in the preceding paragraph do not discuss the manner in which the closures are prepared. Typically in making such closures, the manufacturers of diapers mount rolls of the appropriate tape in their equipment, combining them to form a composite strip of tape, the width of which is substantially the same as the length of the diaper closure to be fabricated. The composite roll is then severed at right angles to the edges of the composite strip at intervals corresponding to the width of the desired tape closure and adhered at an appropriate location along the border adjacent the sides of the diaper. Although this manufacturing process is effective, many relatively small manufacturers are unable to provide the machinery necessary to accomplish the superimposition of several rolls of tape. As a result, it is important for a tape supplier to provide the manufacturers with a composite roll, made up of two or more specific tapes from which closures may readily be prepared.
A variety of diapers have been made with resealable tapes or refastenable disposable diapers. Representative are U.S. Patents 4,049,001, 4,055,181, 4,158,363, 4,227,530, 4,296,750, 4,345,597, and 4,369,786; European Patent Application 148,587; and West German Patent No. 3,419,623.
U.S. 4,330,888 discloses a disposable bib or napkin with an upper edge portion carrying a pressure-sensitive adhesive capable of releasably adhering to the clothing or body of a user. British patents 1,320,628 and 1,342,115 disclose adhesive sheets or adhesive composite material which will releasably adhere to itself.
Additional diapers with tape fastening systems are described in U.S. 3,646,937, U.S. 3,848,594, U.S. 3,874,386, U.S. 3,951,149, U.S. 3,987,793, U.S. 3,999,546, U.S. 4,014,339, U.S. 4,014,340, U.S. 4,020,842, U.S. 4,041,949, U.S. 4,074,004, U.S. 4,194,507, U.S. 4,207,895, U.S. 4,209,016, U.S. 4,237,889, U.S. 4,573,986, and U.S. 4,578,071.
A wide variety of refastenable diapers have been constructed with varying degrees of success. One type of product has a one-piece pressure sensitive tape tab system which permits multiple fastening and refastening of the pressure-sensitive diaper tape tab to the embossed thermoplastic film used as the outside or backsheet of the diaper.
An object of this invention is to provide a resin composition for making an embossed thermoplastic film backsheet which with a suitable fastening tape can be fastened and refastened as many times as desired.
It is an important object of the present invention to provide a thermoplastic resin composition for making an embossed monolayer thermoplastic film which may be effectively utilized as the outside or backsheet of refastenable disposable diapers having a refastenable diaper backsheet film having improved tensile strength.
Another object of the invention is to provide a thermoplastic resin composition suitable for making a refastenable backsheet which may be either blown film constructed or cast-film constructed.
Other objects and advantages of the invention will be more readily apparent from a reading of the description hereinafter.